Conway et al. (J. of Appl. Polym. Sc., 80, 1155-1161, 2001) assumed that a high ratio of glycolide in a Poly(lactic-co-glycolid acid) copolymer (PLGA) may in general reduce its solubility in supercritical carbon dioxide.
Kongsombut et al. (Korean J. Chem. Eng., 25(4), 838-845 (2008) describes the formation of deagglomerated PLGA particles and PLGA-coated ultra-fine powders by rapid expansion of a supercritical carbon dioxide solution with ethanol as co-solvent. The PLGA polymer used was Poly(lactic-co-glycolic acid) with a PLA:PGA ratio of 85:15 and a Mw of 50.000-75.000. The PLGA was dissolved in supercritical carbon dioxide with ethanol as co-solvent in a stirred high-pressure reactor. Rapid expansion from that reactor took place through a nozzle which sprayed the solution onto a target plate or microgrid for analysis purposes. By this so-called RESS-process PLGA microparticles could be obtained which particle size could be controlled by the amount of the co-solvent ethanol added. Particle sizes ranged from about 50 to 500 nm. Furthermore ultra-fine powders from SiO2 or TiO2 were used as simulated core particles that could be coated with the PLGA in that process. The authors conclude that the RESS process with a co-solvent could be a promising enviromentally friendly technique for coating CO2-insoluble ultra-fine drug particles with a high molecular-weight polymer with limited solubility in CO2.
Mishima et al. (AlChE Journal, April 2000, vol. 46, No. 4, 857-865) described the microencapsulation of proteins by rapid expansion of a supercritical carbon dioxide solution with a non-solvent. Several polymers, among them a PLGA derivative, were dissolved in supercritical carbon dioxide with ethanol as co-solvent in a stirred high-pressure reactor. Rapid expansion from that reactor took place through a nozzle which sprayed the solution onto a target plate for analysis purposes. The PLGA polymer used was Poly(DL-lactic-co-glycolic acid) with an approximate weight fraction of glycolide of 50% and a Mw of 5.000. Particles consisting of a lysozyme or a lipase core coated with PLGA could be obtained by that so-called RESS process. The primary particle diameter of the coated particles was 22 μm with a standard deviation of around 1.65.